1. Field of the Invention
The present invention relates to a process for the wet chemical treatment of a semiconductor wafer in a vessel, in which the semiconductor wafer is brought into contact with a liquid in which very small gas bubbles are dispersed.
2. The Prior Art
During the wet chemical treatment of semiconductor wafers with a liquid, it is generally necessary to ensure that the liquid acts uniformly on the surface of the semiconductor wafer. This requirement is important in particular for the wet chemical etching of a semiconductor wafer. Since semiconductor wafers are advantageously etched not individually, but rather in batches, it is difficult to achieve uniform action of the etchant everywhere on the surface of the semiconductor wafer. Uneven etching immediately becomes apparent on comparing measured values which describe the planarity of the semiconductor wafer and are determined before and after etching.
EP-625 795 B1 discloses having a liquid in which extremely fine gas bubbles are dispersed to flow onto semiconductor wafers. For this purpose, the liquid is intensively mixed with a gas before it enters a treatment chamber. It has been found that with this process it is almost impossible to keep the concentration of the gas bubbles constant over a prolonged period. Moreover, with this process it is only possible to maintain for an insufficient extent, the desired laminar flow of liquid in the treatment chamber.
It is therefore an object of the present invention to create a remedy to these problems and to provide a more advantageous process.
The present invention achieves this object and relates to a process for the wet chemical treatment of a semiconductor wafer in a vessel, in which the semiconductor wafer is brought into contact with a liquid in which very small gas bubbles are dispersed. Two circuits are set up for conveying the liquid, with one circuit between a reservoir and the vessel, for conveying the liquid from the reservoir to the vessel and back to the reservoir. Another circuit is from the reservoir back to the reservoir, in order to mix the liquid with a gas on the way back to the reservoir, so that the gas bubbles can form.
The process of the invention has the advantage that the wet chemical treatment of a semiconductor wafer occurs more evenly over the entire wafer surfaces. The outlay involved in making existing treatment apparatus suitable for the process is low.
It is preferable for the gas bubbles to be produced, in the manner described in the abovementioned patent, with the aid of a feed pump. The feed pump draws in the liquid and the gas and
then disperses the gas into the liquid in the form of extremely small gas bubbles. Preferred feed pumps are centrifugal pumps or axial-flow pumps, which result in intensively mixing of the gas and the liquid.
However, the gas bubbles may also be produced by dissolving the gas into the liquid under increased gas pressure and then by reducing the pressure of the pressurized liquid or with the aid of a static mixer or mixers.